Method for Extracting Gas from Liquid

ABSTRACT

A method for extraction of gas from liquid provides for reliable and accurate extraction of gases dissolved in fluids and routing the extracted gas to an analytical instrument. An extraction module comprises one or more fluorosilicone membranes molded into the shape of a flattened disk. The membranes are retained in a housing in a spaced apart relationship. The membrane is permeable to target gas(es), but not to the fluid. Porous support members support the membranes and prevent damage to them and the housing defines separate fluid flow paths for the fluid and the gas extracted from it. Fluid is passed over the membrane in a first fluid phase; target compounds in the fluid diffuse across the membrane to a second fluid phase until equilibrium is achieved.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for extractingdissolved gases from liquid, and more particularly, the inventionrelates to an apparatus for extracting gases dissolved in electricalinsulating oils.

BACKGROUND OF THE INVENTION

The electric power industry has for many years recognized that thermaldecomposition of the oil and other insulating materials withinoil-insulated electrical apparatus can lead to the generation of anumber of “fault gases. These phenomena occur in equipment such as oilfilled transformers (both conservator and gas-blanketed types), load tapchangers, transformer windings, bushings and the like. The presence offault gases may be a measure of the condition of the equipment. As such,detection of the presence of specific fault gases in electricalapparatus, and quantification of those gases can be an important part ofa preventative maintenance program.

The presence of fault gases in oil-blanketed transformers withconservators and other utility assets has well documented implicationsrelating to the performance and operating safety of the transformer.There is a substantial body of knowledge available correlating thepresence of gases with certain, identified transformer conditions andfaults. It is therefore beneficial to monitor the condition ofdielectric fluids in electric equipment as a means to maximizeperformance, and at the same time minimize wear and tear on theequipment, and to thereby minimize maintenance costs and down time.Thus, information relating to the presence or absence of certain faultgases in transformer oil can lead to greatly increased efficiency in theoperation of the transformer.

As an example, it is known that the presence of certain fault gases intransformer oil can be indicative of transformer malfunctions, such asarcing, partial or coronal discharge. These conditions can cause mineraltransformer oils to decompose generating relatively large quantities oflow molecular weight hydrocarbons such as methane, in addition to somehigher molecular weight gases such as ethylene and acetylene. Suchcompounds are highly volatile, and in some instances they may accumulatein a transformer under relatively high pressure. This is a recipe fordisaster. Left undetected or uncorrected, equipment faults can lead toan increased rate of degradation, and even to catastrophic explosion ofthe transformer. Transformer failure is a significantly expensive eventfor an electric utility, not only in terms of down time and the costs ofreplacement equipment, but also in terms of the costs associated withlost power transmission. On the other hand, by closely monitoringdissolved gases in transformer oil, the most efficient operatingconditions for a given transformer can be actively monitored and thetransformer load may be run at or near its optimum peak. Moreover, whendangerous operating conditions are detected the transformer can be takenoff line for maintenance.

Despite the known need for reliable equipment to monitor gas in oil,designing equipment that holds up to the rigors of on-site conditionshas been problematic for a variety of reasons. That said, there are anumber of solutions known in the art. For example, mechanical/vacuum andmembrane extraction methods and apparatus for degassing transformer oilare well known, as exemplified by U.S. Pat. No. 5,659,126. This patentdiscloses a method of sampling headspace gas in an electricaltransformer, analyzing such gases according to a temperature andpressure dependent gas partition function, and based on the derivedanalysis predicting specific transformer faults.

An example of a gas extraction apparatus that relies upon a membranetube for extraction of gas from transformer oil is disclosed in U.S.Pat. No. 4,112,737. This patent depicts a plurality of hollow membranefibers, which are inserted directly into transformer oil in thetransformer housing. The material used for the membrane is impermeableto oil, but gases dissolved in the oil permeate through the membraneinto the hollow interior of the fibers. A portable analytical devicesuch as a gas chromatograph is temporarily connected to the probe sothat the test sample is swept from the extraction probe into theanalytical device for analysis.

Although these devices have provided benefits, there are numerouspractical problems remaining to the development of reliable apparatusfor extraction, monitoring and analysis of fault gases in transformeroils. Many of these problems relate to the design of reliable fluidrouting systems that are redundant enough to provide a relativelymaintenance free unit. Since transformers are often located inexceedingly harsh environmental conditions, fluid routing problems aremagnified. This is especially true given that the instruments needed toreliably analyze the gases are complex analytical instruments. Twopatents that describe the difficulties of these engineering challengesare U.S. Pat. Nos. 6,391,096 and 6,365,105, which are owned by theassignee of this invention and both of which are incorporated herein bythis reference. These two patents illustrate not only the complexitiesof the fluid routing systems needed, but solutions that have proved veryreliable.

One of the most critical points in the analytical process is theextraction apparatus, where gas is actually separated from theelectrical insulating oil. While there are several known apparatus foraccomplishing this task, experience has shown that the extractor is onepoint where failure can occur. Stated another way, extraction devices todate have been more fragile than desired and cannot fully withstand theextreme conditions that are routinely encountered in field applications.As a result, additional support equipment or operation constraints areadded to compensate for the performance shortcomings and to protect theextraction technology, which adds considerably to the cost. Despiteadvances in the technological solutions surrounding the extractiondevices, especially those described in the '096 and '105 patents, thereis a need for an extractor that is reliable and performs accuratelyunder all conditions for substantial lengths of time without beingmonitored.

SUMMARY OF THE INVENTION

The advantages of the present invention are achieved in a firstpreferred and illustrated embodiment of a gas extraction apparatus thatprovides for reliable and accurate extraction of dissolved gases and forfluid-tight handling of both oil and extracted gas. The apparatusutilizes an extraction module comprising paired fluorosilicone membranedisks held in a housing. The membranes are permeable to target gas, butnot to the insulating oil. The housing defines isolated oil and gas flowpaths. The extraction module is connected to an analytical instrumentsuch as a gas chromatograph for qualitative and quantitative analysis ofthe extracted gases.

In alternative embodiments, the extraction module may be built withmultiple pairs of membrane disks, or a single membrane disk.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its numerous objects andadvantages will be apparent by reference to the following detaileddescription of the invention when taken in conjunction with thefollowing drawings.

FIG. 1 is a simplified block diagram showing a system incorporating agas extraction apparatus in accordance with the present invention.

FIG. 2 is a simplified block diagram showing the gas extractionapparatus according to the present invention with significant othercomponents with which the gas extraction apparatus is used.

FIG. 3 is a perspective view of a preferred embodiment of the gasextraction apparatus according to the invention.

FIG. 4 is an exploded perspective view of the gas extraction apparatusshown in FIG. 3.

FIG. 5A is plan view of a membrane separation disk of the type used inthe gas extraction apparatus.

FIG. 5B is a perspective view of the membrane separation disk shown inFIG. 5A.

FIG. 6 is a cross sectional view of the membrane separation disk takenalong the line 6-6 of FIG. 5A.

FIG. 7 is a schematic view of the flow paths for the first and secondphases through the gas extraction apparatus.

DETAILED DESCRIPTION OF PREFERRED AND ILLUSTRATED EMBODIMENTS

The basic environment in which the gas extraction apparatus of thepresent invention is used and the significant components with which itis used will be described generally first to provide context, then amore detailed description of certain components will follow. Withreference to FIG. 1 it may be seen that the gas extractor and analyzer 1of the present invention is contained in a housing 2 that is locatedexternally to the oil-filled or blanketed electrical device 3 that isbeing monitored. Electrical device 3 is typically a conservator or gasblanketed transformer, load tap changer, etc. A sample fluid supply line4 is connected to electrical device 3 and delivers sample fluid to thecomponents contained in housing 2. A sample fluid return line 5 likewisereturns sample fluid to the electrical device from the analyzer 1.Extractor/analyzer 1 has been designed to be operable over extendedperiods of time without maintenance.

Following generally the flow of sample fluid within housing 2, fluid isrouted into extractor assembly 10. Sample containing fluid (i.e. oil)flows through extractor assembly or module 10 in a manner detailedbelow, where gas dissolved in the oil is extracted into a second fluidphase for further processing. The oil from which gas has been extractedis returned to electrical device 3 through fluid return line 5. The gasthat is extracted from the oil may be analyzed to determine the natureof the gases in the oil, or the extraction apparatus may be used toremove contaminants from the oil and thereby purify the oil.

Sample line 4 is preferably attached to electrical device 3 at a pointof high oil flow to insure that a representative sample of fluid isalways provided to extractor assembly 10. The location of the connectionof the fluid return line 5 to electrical device 3 is not critical otherthan it being separated by a sufficient distance from the fluid supplyline to not exchange substantially the same fluid. Specifically thefluid sample line can be attached to the oil fill valve on atransformer, a drain valve on an oil radiator, or an oil by-pass loop,for example. The fluid return line, on the other hand, may be attachedto the bottom drain valve to return the oil to the transformer, or othersuitable positions. Typically, there is no need to tap special portsinto the transformer since the oil supply and return lines may be portedinto existing locations.

As described below, the present invention relies upon principles ofdiffusion across a membrane to extract gases from a first fluid phasewhere the dissolved gases are in a relatively higher concentration,compared with a second fluid phase where the gases are in a relativelylower concentration. Typically, the first fluid phase is the transformerinsulating oil and the second fluid phase is the gas volume containedwithin analysis components of the system.

Sample gas extracted from sample fluid flowing through the extractorassembly 10 is routed through tubing 12 to analytical instrument 14,which is an instrument configured for running automated qualitative andquantitative analysis of the gas samples delivered to it. Analyticalinstrument 14 may be one of several kinds of laboratory gas detectioninstrumentation, and is preferably a gas chromatograph that is designedfor installation in a remote location and is automated by the control ofa programmed computer. Analytical instrument 14 is thus referred to onoccasion as gas chromatograph 14. Sample gas from analytical instrument14 may be returned to extractor assembly 10 via tubing 13.

With reference to FIG. 2, analytical instrument 14 is configured to workwith computer systems 26 and external or remote communications equipment32 so that analytical results may be acquired remotely. It should benoted that as used herein in the description of a preferred embodimentthe word fluid refers to gases that flow through the instrument.However, the invention may be used with apparatus that use liquids andtherefore the word fluid relates to any fluid that might be used in, andanalyzed by, an analytical instrument.

As illustrated in FIG. 2, gas chromatograph 14 is fluidly connected to asource of calibration gas (fluid) 16, extractor module 10, which is thesource of a sample for test 18 (i.e., the samples of gas extracted fromoil in electrical device 3 that are to be analyzed), and a carrier fluid20 which typically is supplied as a high pressure inert gas such ashelium. Each of these sources of fluid (in this case the fluid isgaseous) is connected to a distribution manifold assembly, generallyreferenced with numeral 22. The fluid connections between the sourcefluids 16, 18 and 20 are accomplished with appropriate fluid lines 24(which is the connection from calibration fluid 16 to distributionmanifold assembly 22), 25 (the connection from sample for test 18 todistribution manifold assembly 22) and 27 (the connection from carrierfluid 20 to the distribution manifold assembly. These fluid lines arepreferably stainless steel tubing. The fluid lines 24, 25 and 27 arefitted with appropriate passive fittings such as sealed compressionferrule-type fittings and the like. All connections between fluid lines24, 25 and 27 and other components, such as components of distributionmanifold 22, are fluid-tight connections with appropriate gaskets and0-rings and the like.

Distribution manifold assembly 22 does not form a part of the presentinvention and is not described in detail herein. However, a manifoldassembly suitable for use with the present invention is described indetail in U.S. Pat. No. 6,391,096, which as noted above is incorporatedherein by reference. Several components of the invention, includingactive fluid handling and control components are under the activecontrol of a computer 26. Computer 26 is connected to and sends commandsignals to and receives data from components associated withdistribution manifold assembly 22 by way of data lines 28. Computer 26also controls operation of analytical instrument 14 through data lines30. Computer 26 is connected to telephony or other remote or externalcommunications systems equipment 32 so that computer 26 may be operatedfrom a remote location, which thus allows the analytical instrument tobe operated remotely and for data from the instrument to be acquiredfrom a remote location. Computer 26 also controls the extractor controlcomponents which include circuitry and state machines that monitor andcontrol the gas extraction module 10.

The word computer is used generically herein for a programmed devicecapable of controlling operations of extractor assembly 10 and gaschromatograph 14. Computer 26 will be appreciated therefore to encompassany microprocessor, microcontroller or other processor and associatedhardware and software.

Sample aliquots of fluid that are to be analyzed are acquired andcontrolled by the fluid control and handling components ofextractor/analyzer 1 and are injected into a gas chromatograph 14. Thechromatograph 14 shown schematically in FIG. 1 is preferably a dualcolumn chromatograph. The fluid control and handling components ofdistribution manifold assembly 22 fluidly route the sample aliquots toone of the selected separator columns.

Analyte separation in chromatograph 14 is carried on under controlledconditions as is well known in the art. For instance, the separationcolumns in the chromatograph are contained within atemperature-controlled cabinet. Likewise, all components ofchromatograph 14 are contained within appropriate housings, none ofwhich are shown in the figures but which will be understood as beingnecessary to perform reproducible and accurate analysis.

Gas chromatograph 14, as shown schematically in FIG. 2, includes adetector such as a thermal conductivity detector that is under thecontrol of computer 26. Analytes separated in the chromatographiccolumns flow into and through the detector. Fluid flowing through thesystem such as carrier fluid and analyzed sample are exhausted to theatmosphere at exhaust port 34.

Analytical data compiled by gas chromatograph 14 from the analyzedsample is transmitted to computer 26 via data lines 30 where it isfurther processed according to software stored in the computer.Analytical results may then be transmitted from the computer 26 throughremote communications equipment 32 on an automated basis, or the datamay be acquired on prompt from a remote location.

The construction of extractor assembly 10 will now be explained indetail with reference to FIGS. 3 and 4. At times, relative directionalterms are used to describe the extractor assembly 10 and the positionsof various components relative to other structures. Thus, the word“inner” or “inward” refers to the structural or geometric center of theextractor assembly 10. The word “outer” refers to the direction awayfrom the geometric center. An “inner-facing” surface is a surface thatfaces the center of the assembly, and so on. Referring to FIG. 3,assembly 10 includes a generally cylindrical housing 50 that includes afirst plate 52, a second plate 54, and a scarfing ring 56 sandwichedbetween the first and second plates. As detailed below, there areseveral component parts contained in housing 50, including thecomponents that facilitate extraction of gas from the electricalinsulating oil that is fed into extractor assembly 10, and various fluidflow paths for oil and extracted gas. An oil pump 58 is mountedcentrally to second plate 54 with bolts 55 such that the pump controlsthe flow of oil through the extractor assembly 10. Also mounted tosecond plate 54 is a gas pump 60. An oil temperature sensor 62 ismounted to a side of second plate 54 and provides a means to monitor thetemperature of oil or other fluid in the housing 50—the temperaturesensor is threaded into a cooperative threaded opening in the housing.Temperature sensor 62 is preferably a standard thermocouple but could beany appropriate temperature sensing device. Finally, an oil pressuretransducer 64 is mounted to a side of the second plate 54 so that theoil pressure in housing 50 may be monitored on an ongoing basis. Thetransducer also is threaded into a threaded opening in the housing. Allof the foregoing components are attached to and under the control of thecomputer 26.

Shown schematically in FIG. 3 because the “lower” side of first plate 52housing 50 is not visible in the perspective view of the drawing are anoil inlet 66 and an oil outlet 68 that are both connected to first plate52. Oil inlet 66 is connected to oil sample fluid line 4 and oil outlet68 is connected to oil sample return line 5. As detailed below, oil fromelectrical device 3 flows in a loop beginning with the electricaldevice, delivered through sample line 4 to extractor assembly 10 wheregas in the oil is extracted, flows through housing 50, and is thenreturning to the electrical device via return line 5. Similarly, a gasinlet 70 and gas outlet 72 are attached to second plate 54. The oil andgas inlets and outlets just described are standard fittings that arethreaded into the first and second plates, respectively. Gas inlet 70 isconnected to tubing 13 and is thus the return line from analyticalinstrument 14. The gas outlet 72 is connected to tubing 12 and definesthe sample delivery line to the analytical instrument. The gas extractedfrom oil flowing through extractor assembly 10 is pumped with gas pump60 through outlet 72, through tubing 12 to analytical instrument 14, anddepending upon the state operation, may be returned to extractorassembly 10 via tubing 13 and inlet 70.

All fittings and connections to housing 50 are leak free and utilizeappropriate fittings and fluid-tight seal components such as O-rings andthe like to ensure that there are no leaks.

Turning now to FIG. 4, components of extractor assembly 10 will bedescribed in detail. As noted previously, the primary components ofhousing 50 are first plate 52, second plate 54 and scarfing ring 56.Each of first and second plates 52 and 54 have fluid flow paths definedthrough them in the manner and for the purposes detailed below.Immediately adjacent first plate 52 is first frit 74. First frit 74 is aporous disk material through which oil and/or other liquids readilyflow. Frit 74 is preferably sintered bronze but may be fabricated fromother porous materials including sintered glass, sintered metals, orwire mesh and other materials. In the assembled extractor assembly 10the first side 76 of first frit 74 is sealed around a perimeter thereofwith adhesive to a cooperative seat 77 on the inner-facing side of firstplate 52. Alternately, the seal between the first frit and the firstplate may be facilitated with pressure applied between the two when theextractor assembly is bolted together. Adjacent first frit 74 is firstmembrane 78, which is attached and sealed around its perimeter in themanner described below to scarfing ring 56.

Identical components are stacked in a mirror image of those justdescribed on the opposite side of scarfing ring 56. Thus, withcontinuing reference to FIG. 4, a second membrane 86 is attached andsealed around its perimeter to scarfing ring 56. A spacer layer 82 ispositioned between first membrane 78 and second membrane 86. Spacerlayer 82 provides a physical separation between the two membranes and isporous and inert to the analyte gases. The spacer layer 82 is preferablya porous paper material that is not degraded by the kinds of gases thatare extracted from oil in the system described herein; filter-typepapers have been found to work well but there are numerous othermaterials such as cotton and other fibrous pads that will work. Thespacer layer 82 physically separates the two adjacent membranes 78 and84 and thereby defines a space through which gas extracted from oil mayflow, as detailed below.

A second frit 88, which is an identical material to that described abovewith respect to first frit 74 is attached to second plate 54, again in amanner identical to that described above with respect to first frit 74.

The components just described and shown in exploded format in FIG. 4 aresandwiched together in the assembled extractor 10 with a series of bolts90 (one of which is shown in FIG. 4) around the perimeter of the plates52 and 54. A first O-ring 80 between first plate 52 and scarfing ring56, and a second O-ring 84 between second plate 54 and the opposite sideof scarfing ring 56 insure that the extractor assembly 10 is leak-freewhen assembled. In addition, the O-rings reduce oxygen permutation fromaround the perimeter of the membranes 78 and 86 by isolating themembranes from the atmosphere.

The first and second membranes 78 and 86, respectively, will now bedescribed with particular reference to FIGS. 5A, 5B and 6. Membranes 78and 86 are preferably fabricated from a flexible material that isreadily permeable to hydrocarbons having small molecular weight of thekind that are of interest to the present invention but which isimpermeable to electrical insulating oils. The preferred material is afluorosilicone material, which is very stable in a hydrocarbonenvironment such as electrical insulating oils. The membrane 78 ismolded by pressing fluorosilicone material that has been blended withpolymerizing agents into a mold. The polymerized membrane is removedfrom the mold and is cured by baking at elevated temperatures.

More specifically, a predetermined mass of fluorosilicone material ispreformed into a flattened disk. This pancake-shaped disk is theninserted into a compression mold where it is heated, squeezed andpressed into a very thin disk shape having the thickness attributesdesired. The mold is maintained at an elevated pressure and temperatureuntil the fluorosilicone material cures, at which time the part isremoved from the mold.

The membrane 78 defines a generally flattened circular disk that has alip 100 defined around the outer peripheral edge 102. As best shown inFIG. 6, the outer peripheral edge 102 of membrane 78 is relativelythicker than the central portions of the membrane. The thickness of themembrane is greatest near the outer peripheral edge and gradually isreduced moving toward the center of the membrane. The membrane materialis thus relatively thicker at a peripheral portion 106 where the typicalthickness is about 0.020 inches. The thickness of the membrane graduallydecreases moving inwardly across the central portion 108 of the membranetoward the center of the membrane, where the membrane material isthinnest, typically about 0.004 inches.

The lip 100 is configured to attach and seal to a cooperatively formedlip 104 on the inner-facing periphery of plates 52 and 54 (FIG. 4).Thus, on FIG. 6 the area of lip 104 of scarfing ring 56 to which lip 100on the membrane 78 attaches is shown schematically with dashed lines.When membrane 78 is attached to plate 52, the membrane is stretchedslightly so that the membrane material is slightly taught. This improvesthe fluid seal between the membrane and the plate to which it isattached, and removes any folds, wrinkles or creases in the membrane,which could cause a rupture or tear in the ultra-thin membrane web.Stretching the membrane in this manner thus improves the resistance ofthe membrane to development of leaks.

Extractor assembly 10 is assembled with the components described abovein the manner shown in FIG. 4 with bolts 90 so that the assembly ishermetically sealed and provides fluid-tight and leak free connectionsin all respects. Turning now to FIG. 7, which is highly schematic inorder to show the various flow paths, plates 52, 54 and scarfing ring 56define fluid flow paths through which oil and gas separated from the oilin the extractor assembly 10 flows. The flow paths through plates 52, 54and scarfing ring 56 are defined by bores drilled through the plates.When the plates are assembled, the bores in the plates align andregister with bores in the scarfing ring. O-rings are used to insurethat the bores are leak free to define flow paths that are sealed.

Oil is delivered from electrical device 3 through sample line 4 and intoextractor assembly 10 via oil inlet 66 and by virtue of operation ofpump 58, which is fluidly connected to the oil bores through extractorassembly 10. In FIG. 7, the oil flow path through extractor assembly 10is illustrated in dashed, relatively heavy, bold lines with solidarrowheads illustrating the general flow route. The oil flow path isassigned reference number 111. As noted previously, frit 74 is sealed tofirst plate 52 around the periphery of the frit disk, although thisstructural feature is not evident in the highly schematic view of FIG.7. This defines a space 110 between the surface of the inner-facing side76 of the frit 74 and outer-facing side of membrane 78 into which oilflows. The oil, which is under positive pressure by virtue of operationof pump 58, flows through the center of frit 74 and then across thefacing surfaces of the frit and membrane 78. The oil tends to flowoutwardly from the center of the membrane toward the outer periphery ofthe membrane and frit. A perimeter groove 114 located on theinner-facing surface of first plate 54 accumulates the oil. After theoil flows across the surface of membrane 78 and is returned to thetransformer via bores that register with bores in scarfing ring 56 andfirst plate 52. The oil flow path 111 continues on the opposite side ofscarfing ring 56 into second plate 54 and into a space 116 between theinner-facing surface of frit 88 and the outer-facing surface of secondmembrane 86. As with first frit 74, frit 88 is readily permeable to oil,and the oil flows through the frit and along the surface of the secondmembrane 86. Again, the oil tends to flow outwardly from the center ofthe membrane toward the outer periphery of the membrane and frit wheregroove 120 on the inner-facing surface of second plate 54 accumulatesthe oil. Oil flows through bores in plate 54 and scarfing ring 56 thatthat register with bores in first plate 52 to define a return flow path.The oil thus returns in a loop through first plate 52, through outlet 68and to electrical device 3 by return line 5.

The oil flow through extractor assembly 10 defines a first phase. Gasextracted from the oil in the first phase forms a second phase; the flowpath for the gas is illustrated in FIG. 7 with relatively lighter dashedlines with line-style arrow heads and is assigned reference number 130.

If a diffusion gradient is created across the two different phase sides,which are separated by first membrane 78 and second membrane 86,compounds of interest that exist in a higher concentration on one sideof the membrane will diffuse across the membrane into the second phaseside—the side with the lower concentration of that compound. That is,where oil in the first phase contains contaminants (such as fault gases)that are in relatively higher concentration on the first phase side thanin the second phase, the contaminants diffuse across the phase barrierdefined by the membranes to the second phase side (into the space 122occupied by the porous paper spacer 82). Said another way, thecontaminants in the first phase diffuse across the phase barrier definedby the membranes and into the second phase, where they reliably andreproducibly accumulate and are representative of and proportional tothe concentration of the contaminants in the first phase. This isschematically illustrated by the “bold-line” arrows representing oilphase flow path 111 and the dashed arrows 130 representing the secondphase side, or gas phase flow 130. As oil under pressure circulatesthrough extraction apparatus 10, and more specifically, as the oil flowsalong the surfaces of the membranes, contaminants in the oil diffusethrough the membranes and enter the gas phase 130. The contaminant(i.e., gas) diffusion across membranes 78 and 86 is illustrated withdashed arrows 132. The gas phase flow path 130 is isolated from oilphase flow path 111 and is defined by bores defined in plates 52 and 54,and scarfing ring 56. As noted earlier, spacer 82 between the adjacentmembranes 78 and 86 maintains a space 122 into which the gas diffuses.Gas flow is initiated and maintained by a pump 60(FIG. 4). As best shownin FIG. 7, sample gases from analytical apparatus 14 enter extractorassembly 10 through gas inlet 70 in second plate 54, and into gas phaseflow path 130 through the spacer 82 (gas space 122), through gas pump 60and is exhausted through gas outlet 72 and returned to analyticalapparatus 14.

Operation of the system will now be detailed. As noted, oil flow isinitiated by operation of pump 58, causing oil to flow in a circulatingloop through oil phase flow path 111. As oil flows through the frits 74and 88 and thus past and over the outer-facing surfaces or sides ofmembranes 78 and 86, gas diffuses through the membranes (referencenumber 132) into the space 122, which is defined by the spacer 82, andthus into gas phase flow path 130. The gas phase resulting fromdiffusion of gas molecules from the oil phase into the gas phase flowsin a circulating loop through gas chromatograph 14; gas is circulatedwith the gas pump 60. Circulation of the oil phase and gas phase isallowed to continue until equilibrium in the concentration of gas existson both sides of the phase barriers defined by membranes 78 and 86.

During the normal operation it is possible for the oil phase pressure tobe less than the gas phase pressure. This may occur for several reasons,including aberrations in the operating conditions of the oil pump,external interference, etc. If a negative pressure does occur on the oilphase side, the membranes 78 and 86 tend to be “pulled” toward frits 74and 88, respectively. The frits support the membranes and preventmembrane rupture if the membranes are pulled toward the frits.

Diffusion of compounds across the membranes is driven primarily byconcentration gradients across the membranes. The time required to reachequilibrium or near equilibrium conditions depends upon factors such asgas concentration gradients and temperature, the volume of the gas beingequilibrated, the thickness of the membrane, and the membrane surfacearea that is exposed to the oil. In addition, the flow rate of the oilcarrying the gases affects the diffusion rate and thus the time requiredto reach equilibrium.

As noted earlier, contaminants of interest contained in oil filleddevice 3 are allowed to diffuse from the first liquid phase into thesecond fluid phase in extractor assembly 10. In this regard, during asample equilibrium and acquisition phase oil is continuously circulatedthrough the extractor assembly 10, returning as described earlier to theoil filled device 3. As the oil flows through the extractor assembly,dissolved gas contained in the oil diffuses across the membranes 78 and86 into the second phase. This second phase, which comprises gaseousfluid, is circulated in either set time intervals or continuously toassure that all fluid in the second phase is homogeneous and untilequilibrium conditions are reached. Stated otherwise, principles ofdiffusion dictate that the contaminants in the oil diffuse across themembrane from an area of relatively higher concentration to an area ofrelatively lower concentration until equilibrium (or conditions near toequilibrium) is reached.

As noted above, equilibrium and the rate of diffusion across themembranes are influenced by many different factors. In practice, it hasbeen found that equilibrium using the extractor assembly 10 describedherein is achieved in about 15 minutes with a total nominal gas volumeof less than 7 cm³I. This may be contrasted with the gas extractionapparatus described in the '105 and '096 patents, which required up toand greater than 1 hour with a nominal gas volume of up to 65 ml. It isapparent therefore that the present invention requires magnitudes lesstime to equilibrate, and magnitudes less volume of gas extracted fromthe oil phase than required by the patents just mentioned.

When computer 26 determines that it is appropriate to inject a sample ofgas from the second phase into analytical instrument 14, or whencomputer 26 is prompted to do so externally, the continuous circulatingloop of gas 130 is switched in distribution manifold 22 so that thesample gas is routed to the analytical instrument 14.

Typically simultaneously with the equilibration and sample acquisitionstep, and prior to operation of chromatograph 14, the system allowsequilibration of the chromatograph 14 with pure carrier fluid 20, whichas noted is typically an inert gas such as helium. This allows any fluidin the separation columns to elute and be flushed through the instrumentand to be vented to atmosphere at 34. Sample gas is then injected intothe chromatograph and gases present in the sample are qualitatively andquantitatively analyzed.

In the illustrated embodiment of the extractor 10 described above andshown in the attached drawings, the extractor uses two membranes housedin a housing defined by two plates and a scarfing ring. It will beappreciated that the fluid flow paths through the plates are configuredso that additional pairs of plates, membranes and a scarfing ring may bestacked so that the capacity of the system and its speed increase. Thus,an extractor module may be defined as two membranes, two plates and asingle scarfing ring. Multiple extractor modules may be stacked with thefluid pathways between modules communicating.

Similarly, an extractor module according to the present invention may bemade using a single membrane. In this case, the extractor module isconfigured as shown in the figures with only a single membrane. The oilphase containing contaminants flows over the first side of a singlemembrane and the contaminants diffuse through the membrane 78 into aspace defined by a spacer layer 82 that is positioned on the oppositeside of membrane 78, thereby defining the physical separation betweenthe single membrane 78 and the opposite wall of the module housing. Aswith the embodiment of FIG. 4, the spacer layer 82 physically separatesthe single membrane 78 from the adjacent wall of the module housing andthereby defines a second phase space through which gas extracted fromoil may flow.

In view of the many possible embodiments to which the principles of ourinvention may be applied, it should be recognized that the detailedembodiments are illustrative only and should not be taken as limitingthe scope of the invention. Rather, we claim as our invention all suchembodiments as may come within the scope and spirit of the followingclaims and equivalents thereto.

We claim:
 1. A method of removing gas in a first fluid phase and routingthe removed gas into a second fluid phase, comprising the steps of: a)defining a first fluid flow path through a housing; b) defining a secondfluid flow path through the housing, the second fluid flow path beingisolated from the first fluid flow path; c) installing a separatormembrane in the housing such that the separator membrane separates thefirst and second fluid flow paths and such that the separator membraneis in a stretched condition and has a variable thickness; d) causing afirst fluid containing target compounds to flow through the first fluidflow path and over a first side of the separator membrane, and causing asecond fluid to flow through the second fluid flow path and over asecond side of the separator membrane, wherein the first fluid is at ahigher pressure than the second fluid; and e) causing target compoundsfrom the first fluid to pass through the separator membrane and routingsaid target compounds into said second fluid flow path.
 2. The methodaccording to claim 1 including continuing steps d and e until theconcentration of target compounds in the second fluid is at equilibriumwith the concentration of target compounds in the first fluid.
 3. Themethod according to claim 1 including the steps of routing the secondfluid to an analytical instrument and operating the analyticalinstrument to obtain data comprising quantity and quality data about thetarget compounds.
 4. The method according to claim 3 wherein theanalytical instrument is a gas chromatograph.
 5. The method according toclaim 4 including the step of transmitting the data to a remotelocation.
 6. The method according to claim 1 including the step ofinterposing a second separator membrane between the first and secondfluid flow paths wherein each of said membranes has a first and secondside and both of said membranes are spaced apart with the second side ofthe first membrane facing the second side of the second membrane todefine a space between said first and second membranes and wherein thesecond fluid flow path is in the space.
 7. The method according to claim1 wherein the step of installing the separator membrane in a stretchedcondition entails applying tension to the separator membrane.
 8. Themethod according to claim 1 including the step of supporting theseparator membrane by interposing a porous membrane support member alongone side of said separator membrane.
 9. The method according to claim 6including the step of installing a spacer between the second side of thefirst membrane facing the second side of the second membrane to definethe space therebetween, and wherein the spacer is porous and inert tofluid carried in said space.
 10. The method according to claim 1 whereinthe separator membrane defines a generally flattened disk that has avariable thickness where the first fluid flows over said separatormembrane.
 11. The method according to claim 10 wherein the separatormembrane is thicker at a peripheral portion of said flattened disk andthinner at the center of the flattened disk.
 12. The method according toclaim 11 wherein the separator membrane is a fluorosilicone material.14. A method of removing gas in a first fluid phase and routing theremoved gas into a second fluid phase, comprising the steps of: a)delivering under positive pressure a first fluid a containing aconcentration of a target compound to a first fluid flow path, saidfirst fluid flow path including a flow section that passes over a firstside of a membrane defining a generally flattened disk that is thickerat peripheral portion thereof and thinner at the center of the flatteneddisk, said membrane further defining a selectively porous barrierbetween said first fluid flow path and a second fluid flow path; b)causing a second fluid in the second fluid flow path to flow over asecond side of said membrane; c) allowing said target compound todiffuse across said membrane from said first fluid flow path to saidsecond fluid flow path; d) continuing step c) until the concentration ofthe target compound in the first fluid flow path is in equilibrium withthe concentration of the target compound in the second fluid flow path.15. The method according to claim 14 including the step of deliveringthe equilibrated fluid in the second fluid flow path to an analyticalinstrument to quantify the concentration of the target compound in thesecond fluid.
 16. The method according to claim 15 wherein the firstfluid is an electrical insulating oil and the second fluid is a gasphase.
 17. The method according to claim 14 including the step ofcausing the positive pressure of the first fluid to become negativepressure, and further including the step of supporting said membranewith a porous support member positioned adjacent the first side of saidmembrane.
 18. A method of removing gas in a first fluid phase androuting the removed gas into a second fluid phase, comprising the stepsof: a) withdrawing fluid defining said first fluid phase from anelectrical device; b) causing said fluid to flow through a first flowpath and over a selectively porous fluorosilicone membrane, said firstflow path being isolated from a second fluid flow path by saidselectively porous fluorosilicone membrane and wherein said selectivelyporous fluorosilicone membrane has a variable thickness where said fluidflows over said selectively porous fluorosilicone membrane; c) allowinggas in the fluid phase to diffuse across said selectively porousefluorosilicone membrane from said first fluid flow path to said secondfluid flow path until the concentration of gas in said second fluid flowpath is in equilibrium with the concentration of gas in said insulatingfluid; d) analyzing the gas in said second fluid flow path.
 19. Themethod according to claim 18 including stretching the selectively porousfluorosilicone membrane so that it is under tension.
 20. The methodaccording to claim 19 including forming the selectively porousfluorosilicone membrane with a thicker peripheral portion and arelatively thinner central portion.